7 BIO 326R Growth - BIO 326R Growth and control Growth Can...

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BIO 326R Growth and control
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Growth Can be an increase in size of organism or increase in the number of organisms. We’re mostly concerned with number of organisms Measurement Calculate CFU by plating Absorbance (OD 600 ) – can measure dead cells Measure DNA synthesis, or consumption of nutrients - difficult to do To grow or not to grow Easy decision for most microbes – if nutrients, temperature and water are present, growth will usually occur
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Growth Synthesis of new cell components DNA replication Ribosomes Lipid membranes Most energy intensive Cell wall
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Growth curve for bacteria in liquid  media lag log stationary death CFU time
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Lag Phase Some time needed to sense new favorable growth conditions Old cell with depleted ATP, ribosomes etc.- more time needed to synthesize these, can result in a longer lag phase Change in nutrients – need new enzymes for new substrates Oxidized or otherwise damaged components need to be replaced In lab conditions, this is almost always seen when stored E. coli samples are grown. E. coli is often stored at +4C for short terms, and -20C or -80C for long terms. The cultures stored at -20 or -80 are usually put in a special media (rich in glycerol) to prevent killing by ice crystallization. The +4C cultures lag time will vary considerably depending on how long they’ve been stored. The -20 to -80C cultures usually have consistent lag times.
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Log Phase – exponential growth Total population has a defined doubling (generation) time Growth must be “balanced” among all cellular components Ratio of fat:lipid:protein:nucleic acid will be constant within the population Shifts in medium (nutrients) will induce a lag Cells must adjust enzymes to new environment e.g. bacteria in a medium with glucose as energy source remove glucose and replace with lactose Cells will lag until lactose-metabolizing enzymes are made in sufficient quantities This is an example of “unbalanced” growth. Once the enzymes have been made, the population will resume log phase (and balanced growth).
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Stationary phase Most bacteria probably spend most of their time in this state Most research is on log phase cells Cultures reach stationary phase at about 10 9 cfu/ml Cells that have been starved of nutrients and reached stationary phase are often more difficult to kill. They’re “tough.” Cell death = cell division (number of cells remains the same) Both could be zero (how can you tell?) i.e. Stationary phase can be explained by 100 cells dying and 100 cell divisions. Or by no cells dying at
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This note was uploaded on 07/24/2009 for the course BIO 52035 taught by Professor Edsatterwhite during the Spring '08 term at University of Texas at Austin.

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7 BIO 326R Growth - BIO 326R Growth and control Growth Can...

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